Identification of polyolefin-based materials which function equivalently to conventional engineering thermoplastics (ETPs) for structural applications, particularly as automotive materials, would be commercially and economically advantageous. Polyolefins possessing the necessary properties to function as ETPs could compete against existing ETP materials (polycarbonates, polyurethanes, styrene-acrylonitrile and styrene-acrylonitrile-butadiene copolymers, etc.) in terms of price vs. performance. The development of such “structural polyolefins” (SPOs) would thus be highly desirable.
Ethylene-dicyclopentadiene copolymers (EDCPDs) are attractive as a potential basis for development of SPOs. It is possible to tailor the properties of such copolymers by means of appropriate selection of polymerization catalysts. EDCPD materials are typically amorphous materials possessing good optical properties and relatively high glass transition temperatures (Tgs). Many thermal and mechanical properties for neat EDCPDs and other cyclic olefin copolymers (COCs) are competitive with those of commercial ETPs and polypropylene-based materials.
EDCPD copolymers offer the unique advantage, as compared to PP-based materials and COC materials based on monoolefinic comonomers such as norbornene, of facile property adjustment, alteration and tailoring by means of post-polymerization chemical derivatization (hydrogenation, epoxidation or other functionalization, etc., with or without ring opening) of the pendant DCPD cyclopentenyl double bond which remains in the chemical structure after the copolymer is formed. Functionalization can be used to improve and tune resin properties such as compatibility with other polymers, paintability, adhesion, and filler interactions in compounding. Ethylene-DCPD copolymers are therefore attractive as potential novel ETPs for a number of reasons.
It is desirable for EDCPD copolymers which are to ultimately be used to prepare structural polyolefins to have relatively high Tg values. Generally speaking, the Tg of a polymeric material is the temperature below which the molecules in its amorphous phase have very little mobility. On a macroscopic scale, polymers are rigid below their glass transition temperature but can undergo plastic deformation above it. Thus, it is desirable that a material utilized for structural applications where dimensional heat stability is required to have a Tg sufficiently high to prevent plastic deformation at its use temperatures.
It is also desirable that Tg values of such materials, while being sufficiently high for structural uses, are not needlessly high. Melt-processing and -blending techniques used to manipulate polymers and to fabricate molded articles, such as injection molding and extrusion, require heating of a polymer above its Tg (in the case of an amorphous material) to allow the polymer to flow. For a semicrystalline polymer, heating above its melting point (Tm) to liquefy any crystalline domains is also required to form a processable polymer melt. At higher Tg values for a polymer, higher processing temperatures are required, resulting in a greater use of energy and higher processing costs and also resulting in a greater risk of thermal decomposition of the polymer. It is therefore desirable to prepare polymers with Tg values that are sufficiently high to permit dimensional stability over a desired temperature use range for a given structural application, yet remain low enough over the minimum required value that processing may be carried out at the lowest possible temperature. For the SPO materials of interest herein, Tg values in the range of 85° C. to less than 130° C. are highly desirable, although temperatures above this range (up to 180 ° C.) are also desirable for certain functionalized materials.
It is also desirable that the Tg value of a polymer may be adjusted in a predictable fashion by varying the polymer's microstructural features, since the desirable end use temperature ranges of structural materials vary according to application. In general, higher Tgs desirably widen the end use temperature range of a material, but undesirably add cost to material processing. Facile adjustment of Tg allows for the selection of SPO materials exhibiting the best price versus performance balance for a particular end use application.
A wide variety of microstructural features may be used to influence the Tg of a polymer or copolymer. In general, the Tg values exhibited by EDCPD copolymers increase as the DCPD content of the copolymer increases. Nevertheless, even for a copolymer with a given DCPD content, it may be possible to further vary and control Tg by adjusting various other structural characteristics. Such features as the nature of comonomer placement along the chain (sequence distribution and degree of random, alternating, or blocky character), tacticity, and stereoconfiguration characteristics of the comonomer (for example, endo-versus exo-DCPD units), and the like, can result in higher or lower Tgs for copolymers of the same compositional makeup. These structural characteristics can, in turn, be adjusted or changed by means of selecting appropriate copolymer preparation procedures. Thus, such factors as polymerization reaction conditions and the nature of the polymerization catalyst used can all play a role in determining copolymer structure and the resulting Tg of such materials.
When considered over a range of compositions, the Tgs of copolymers possessing different microstructures may also exhibit different sensitivities to DCPD content, in the sense that decreasing or increasing the comonomer level by a given amount may produce larger or smaller changes in Tg. In order to prepare materials that best span a Tg range of interest, it is desirable for small changes in comonomer content to provide relatively large changes in Tg. For example, a copolymer composition for which varying DCPD content over a range of 10 mole % produces a change in Tg over a range of 30° C. would be more desirable than a copolymer composition for which varying DCPD content over a range of 10 mole % produces a change in Tg over a range of only 5° C.
It is additionally desirable, for reasons of cost, for the relationship between Tg and DCPD content to require a minimum amount of DCPD to achieve a certain Tg or Tg range. For example, other factors being equal, a copolymer composition that produces Tgs in a given desirable temperature range with only 15-20 mole % DCPD incorporated would be more desirable than a copolymer composition that gave Tgs in this identical temperature range at compositions of 45-50 mole % DCPD.
In addition to the proper selection of Tg and optimal control of Tg by microstructure and/or composition, the appropriateness of a certain polymer's use as an SPO material relies on other properties which are independent of Tg; for example, molecular weight, thermal stability to chemical decomposition, and miscibility with desired tougheners, fillers, etc. In particular, polymers with high molecular weights are desirable as compared to polymers with lower molecular weights, since such materials exhibit greater melt strengths and therefore superior processing capabilities. It is generally desirable to synthesize polymers having the highest possible weight average molecular weight (Mw) and/or number average molecular weight (Mn) achievable at a given composition. It is particularly desirable to synthesize copolymers having Mws of at least 170,000 g/mol (as measured versus polystyrene standards by Gel Permeation Chromatography (GPC) analysis.
The synthesis of EDCPD copolymers using various metallocene or Ziegler-Natta catalysts is known, with a wide range of DCPD molar contents for the copolymers being disclosed. U.S. Pat. No. 6,191,243 discloses EDCPD copolymers useful in optical applications prepared using the zirconocene catalyst μ-(CH3)2C(cyclopentadienyl)(9-fluorenyl)ZrCl2 in conjunction with a borate or methylalumoxane activator. The microstructures of such copolymers are said to have a high level of ethylene-DCPD monomer alternation and to lack DCPD-DCPD dyad linkages and crystalline polyethylene segments. In the exemplified copolymers of the '243 patent, the DCPD content lies within the range of 36 mole % to 46 mole % and the Tg lies within the range of 130° C. to 175° C., with Tg generally increasing with increasing DCPD content. Additional comparative EDCPD copolymers were prepared using a μ-(CH2CH2)bis(1-indenyl)ZrCl2 or a μ-[(CH3)2Si]bis(1-indenyl)ZrCl2 catalyst, having DCPD contents of 35-45 mole % and Tgs of 130-158° C.
The '243 patent also describes the synthesis of a comparative copolymer material having an overall DCPD content of 32 mole % using the μ-(CH3)2C(cyclopentadienyl)(9-fluorenyl)ZrCl2 catalyst. However, this material is described as partially crystalline (exhibiting a melting transition, Tm, in its differential scanning calorimetry (DSC) spectrum) and containing a large fraction of toluene-insoluble material. The toluene-soluble fraction, for which composition was not reported, showed a broad, indefinite Tg at about 114° C.
U.S. Pat. Nos. 6,476,153 and 6,232,407, European Patent Applications No. EP0964005 and EP1266937A1, and Japanese Patent Applications No. JP2000017015A and JP2001329016A also disclose the synthesis of EDCPD copolymers prepared using μ-(CH3)2C(cyclopentadienyl)(9-fluorenyl)ZrCl2. These materials have DCPD contents of about 43-46 mole % and Tgs of about 143° C.-157° C.
Additional catalyst systems have been utilized for the synthesis of similar EDCPD materials. Japanese Patent Applications JP2002302518A1 and JP2003328618A disclose the synthesis of EDCPDs having DCPD contents of 39-48 mole % using trichloro(cyclopentadienyl)titanium. The Tgs for the materials having 46-48 mole % DCPD range from 165-178° C. (no Tg is reported for the 39 mole % material). U.S. Pat. No. 6,627,714 describes the preparation of EDCPD copolymers using various bridged bis(cyclopentadienyl)zirconium catalysts. In general, it is indicated in the '714 patent that the DCPD content in such copolymers may range from 1 mole % to 95 mole %. Specific copolymers are exemplified which range in DCPD content from 47.6 mole % to 59.0 mole %. No Tgs are reported for these materials. The weight average molecular weights (Mws) of the copolymers from Gel Permeation Chromatography (GPC), where reported, range from 92,000 to 235,000; the number average molecular weights (Mns) range from 48,420 to 130,560; and the polydispersity indices (PDI;=Mw/Mn) range from 1.7-1.9. The high Tg and high transparency of such copolymers are said to be advantageous. These disclosed copolymers are useful in lenses, optical disks, optical fibers, etc. The '714 patent also discloses the synthesis of a copolymer having 29.9 mole % DCPD; however, this material is of significantly lower molecular weight than the higher-DCPD materials (Mn 8,030; Mw 49,000; PDI 6.1), and no Tgs is reported.
In summary, EDCPD copolymers having ≧35 mole % DCPD and Tgs of 130° C. are well-known in the art. However, in the art describing these high-DCPD, high-Tg materials, attempts to prepare copolymers having lower DCPD contents have produced either materials of low molecular weight or materials containing significant portions of crystalline (homo-polyethylene) material as evidenced by lowered solubility of a portion of the sample. While small amounts of crystalline or homo-polyethylene material are not detrimental to the properties of an EDCPD copolymer overall, the presence of significant amounts can create problems with respect to phase homogeneity or lowered transparency within the structural polyolefins of interest. Such contamination also complicates characterization of the sample, leads to problems with sample fractionation during functionalization or solution processing, and, by obfuscating the true composition of the copolymer present, complicates the strategy of controlling Tg by manipulating DCPD incorporation.
In some instances, EDCPD copolymers having relatively low DCPD contents have been made that exhibit no detectable Tms, indicating that there is no significant crystallizable polyethylene homopolymer present. [It is noted that copolymers having very low DCPD contents can also exhibit Tms arising from long crystallizable ethylene sequences; however, such materials have Tgs too low to be of interest for the structural uses described herein.] For example, in Naga et al; Polymer 2006, 47, 520-526 it is reported that with the use of a μ-(CH2CH2)bis(1-indenyl)ZrCl2 polymerization catalyst, completely amorphous (Tm-free) EDCPD materials with 24.8-30.5 mole % DCPD have been prepared. Such materials, however, have Tgs of from 65.4° C. to 71.3° C., which temperatures are too low to make such EDCPD materials useful as structural polyolefins. Similarly, Suzuki et al., J. Appl. Polym. Sci. 1999, 72, 103-108 discloses the synthesis of EDCPD copolymers having endo-DCPD contents of 13.2 mole % or less using either a bis(cyclopentadienyl)zirconium dichloride-, μ-(CH2CH2)bis(1-indenyl)ZrCl2—, or μ-Ph2C(cyclopentadienyl)(9-fluorenyl)ZrCl2-based catalyst system. The Tgs of these materials are below 44° C.
Japanese Patent Application No. JP2001031716A discloses the use of the μ-(CH2CH2)bis(1-indenyl)ZrCl2 catalyst to prepare EDCPD copolymers having 16, 27, and 40 mole % DCPD and Tgs of, respectively, 38° C., 84° C., and 135° C. However, these materials are of only moderate molecular weights, with Mws of 104,000-150,000 via GPC (versus polystyrene standards).
U.S. Pat. No. 6,627,714B1 also discloses the use of a μ-(CH2CH2)bis(1-indenyl)ZrCl2 catalyst to prepare copolymers having 38.3-49.5 mole % DCPD, although no Tg or molecular weight characteristics are reported for these polymers. U.S. Pat. Nos. 6,569,800, 6,323,149, and 6,350,831 disclose the synthesis of an EDCPD copolymer having 24.1 mole % DCPD using an unbridged bis(cyclopentadienyl)zirconium catalyst. However, no Tg or molecular weight information was reported for this material. U.S. Pat. No. 6,469,117 discloses the use of trichloro(cyclopentadienyl)titanium and mono(cyclopentadienyl)titanium alkoxide and -amide catalysts to prepare EDCPDs having 3.0-18.7 mole % DCPD, also with no Tg or molecular weight information. U.S. Pat. No. 6,469,117 and U.S. Published Patent Application No. 2003/065118 describe EDCPD copolymers useful in optical applications prepared using monocyclopentadienyl titanium alkoxide and amide complexes as catalysts. Exemplified copolymers have very low DCPD contents, ranging from 12.6 wt % to 52.1 wt % (3.2 mole % to 18.7 mole %); no Tg or molecular weight values are reported.
In summary, considering the known catalytic systems based on titanium and zirconium complexes utilized to prepare EDCDPD copolymers, there are no known copolymers derived from these systems which are free from significant contamination with crystalline homopolymer; have Tgs in the desirable range of 85 to less than 130° C.; and/or have desirably high molecular weights of Mw 170,000 g/mol or more (as measured versus polystyrene standards by GPC analysis).
Li et al. Macromolecules 2005, 38, 6767 discloses the synthesis of EDCPD copolymers containing 35.1-45 mole % DCPD and having Tgs of 101 to 125° C., using a scandium-based catalyst. These copolymers are described as amorphous and strictly alternating in structure, with an isotactic:syndiotactic ratio of incorporated DCPD units of about 40:60. The molecular weights of the copolymers (as measured by GPC versus polystyrene standards) range from Mw 248,520-459,000 g/mol and Mn 107,000-279,000 g/mol (with PDI 2.1-3.1). However, the synthesis of copolymers having Tgs in the remainder of the most desirable range for structural applications, i.e. from 85-100° C. and from 125-<130° C., is not disclosed. Furthermore, in addition to it being desirable to prepare EDCPD copolymers spanning a greater portion of the desirable Tg range, for the cost considerations described above, it would be advantageous for EDCPD copolymers exhibiting Tgs in this desirable range to require a smaller amount of DCPD to achieve a particular Tg [for example, it would be advantageous to prepare a copolymer exhibiting a Tg of 101° C. that contained less than 35.1 mole % DCPD].
Given all of the foregoing considerations, it would be desirable to identify selected ethylene-DCPD copolymer materials, and preferred preparation procedures for making such materials. Such selection would provide copolymers of the ethylene-dicyclopentadiene type which have ideal thermal, rheological, and compositional characteristics to permit economic utilization of such materials to realize engineering thermoplastics. Such EDCPD materials are those which have sufficiently high molecular weights and the optimal and cost effective balance between DCPD content and appropriate Tg values. These materials furthermore would be substantially free of any significant amounts of crystallizable contaminants such as polyethylene homopolymers.
It would also be desirable to provide hydrogenated or functionalized derivatives of such selected EDCPD copolymers which could be tailored to provide useful structural polyolefins.
Since hydrogenated EDCPD copolymers are derived from EDCPDs, the same trends and constraints previously discussed for EDCPD copolymer materials exist for hydrogenated EDCPDs (HEDCPDs). HEDCPDs having high contents of hydrogenated DCPD (HDCPD) units (40 to 46 mole % HDCPD) and high Tgs (140 to 170° C.) are disclosed in U.S. Pat. Nos. 6,191,243, 6,232,407, 6,388,032, and 6,476,153, European Patent Application Nos. EP1266937A1 and EP1028128A1, and Japanese Patent Applications JP2001329016A, JP2000119328A, and JP2002302518A1. These materials are synthesized by RuClH(CO)(PPh3)3- or Co(acac)3-mediated hydrogenation of the EDCPD copolymers derived from trichloro(cyclopentadienyl)titanium, μ-(CH3)2C(cyclopentadienyl)(9-fluorenyl)ZrCl2, and μ-(CH2CH2)bis(1-indenyl)ZrCl2 polymerization catalysts. U.S. Pat. No. 6,191,243 also discloses the synthesis of a hydrogenated material containing 35 mole % HDCPD, but no Tg or molecular weight information is given.
The art concerning HEDCPD copolymers with lower Tgs and/or mole % HDCPD contents indicates that such materials are of limited Tg and molecular weight range. Naga et al. Polymer 2006, 47, 520-526 discloses the synthesis of HEDCPDs having 24.8-30.5 mole % HDCPD and Tgs of 74.8-83.3. The molecular weight of the copolymer having Tg 83.3 is disclosed to be very low, Mw=6,200. Japanese Patent Application No. JP2001031716A discloses the preparation of HEDCPDs having 16, 27, or 40 mole % HDCPD and Tgs of, respectively, “below 100° C.”, 83° C., and 133° C. These materials were derived from EDCPDs synthesized using a μ-(CH2CH2)bis(1-indenyl)ZrCl2 catalyst and having GPC molecular weights (Mw) of 150,000 or less (versus polystyrene standards). Suzuki et al., J. Appl. Polym. Sci. 1999, 72, 103-108 teaches the synthesis of endo-HEDCPD copolymers derived from endo-EDCPDs prepared with a variety of zirconocenes. These materials have very low (4.4 mole % or less) HDCPD contents; no Tgs are reported.
In summary, it would be desirable to prepare HEDCPD copolymers that possess Tgs in the most useful range for structural applications, from 85 to less than 130° C. having high molecular weights (Mw greater than or equal to 170,000 g/mol versus polystyrene standards as measured by GPC analysis) and also substantially free from crystalline material.
Functionalized EDCPD copolymers can also be usefully employed in the preparation of structural polyolefins. One of the most common types of functionalization of these materials containing co-monomers with unsaturation comprises materials prepared by epoxidation of the double bond within such unsaturated co-monomers. Epoxidized EDCPD copolymers are also in general known in the art.
Japanese Patent Application No. JP2001031716A discloses the synthesis of epoxy-EDCPD copolymers having 16, 27, and 40 mole % epoxy-DCPD units and Tgs of, respectively, 56, 112, and 178° C. These materials are derived from EDCPDs synthesized using a μL-(CH2CH2)bis(1-indenyl)ZrCl2 catalyst and having GPC molecular weights (Mw) of 150,000 or less (versus polystyrene standards).
Li et al. Macromolecules 2005, 38, 6767, discussed above, and Hou, Z., Yuki Gosei Kagaku Kyokaishi (J. Synth. Org. Chem., Jpn.) 2005, 63, 1124 disclose the perbenzoic acid epoxidation of an alternating EDCPD copolymer having 45.0 mole % DCPD and Mw 459,000 (via GPC versus polystyrene). The Tg of the epoxidized material is 193° C., a very high value which is disadvantageous for the reasons described in paragraph.
In summary, it would be desirable to prepare epoxy-EDCPD copolymers that possess Tgs in the most useful range for functionalized materials used for structural applications, from 85 to 180° C., having high molecular weights (Mw of 170,000 g/mol or more versus polystyrene standards as measured by GPC analysis) and also being substantially free from crystalline material.